A hydraulic jack is a well-known simple lifting equipment used in mechanical and electrical equipment, vehicle maintenance, earthquake relief, etc. It has such advantages as simple structure, small size, easy operation, high lifting capacity, etc. The existing hydraulic jacks usually adopt the slow lifting mode of increasing top pressure with hydraulic oil increment. The hydraulic oil pump of hydraulic jack is generally composed of a hood, an outer cylinder jacket, a piston rod, a cylinder, a valve body, a large pump core and a small pump core mounted on the valve body, etc. During working, by operating a handle of the hydraulic oil pump, a certain volume of hydraulic oil can be pressed in the inner cavity of cylinder, so as to lift the piston rod.
When the existing hydraulic jack is lifting quickly under no-load condition, the pressure regulating valve of the large pump is adjusted to a low pressure, at this time, the large pump only works under no-load condition, and under the joint action of the large and small pumps, it can achieve quick lifting. When there is load, the pressure regulating valve of the large pump unloads, only the small pump works, and the load is lifted slowly. However, when the existing jack is in a light load condition, only the small pump works, at this time, the jacking speed is slow and the travel time is long, and it is time-consuming and labor-intensive, with low efficiency.